> Dear Dr Case, what you can say about AMBER99SB force field? Is it also
> considered as an "old" force field? It has several parametrization
> improvements toward the Amber99 force field?

No. ff99SB is quite "up to date". If you look in amber10/dat/leap/cmd, you
will see the force fields we currently are recommending for most simulations.
Older force fields are in the "oldff" subdirectory -- they are preserved so
that old results can be checked, are differences investigated. Material in
the "oldff" directory are not generally recommended for new simulations.

Of course, there is some subjectivity here, and the opinions of the Amber
devleopers are not definitive. This is still research.